Methods of producing plane-parallel structures of silicon suboxide, silicon dioxide and/or silicon carbide, plane-parallel structures obtainable by such methods, and the use thereof

ABSTRACT

A product produced in a PVD method is described, which consists of thin plane-parallel structures having a thickness in the range from 20 to 2000 nm and small dimensions in the range below one mm. Production is carried out by condensation of silicon suboxide onto a carrier passing by way of the vaporisers. The carrier is pre-coated, before condensation of the silicon suboxide, with a soluble, inorganic or organic separating agent in a PVD method. All steps, including that of detaching the product by dissolution, can be carried out continuously and simultaneously at different locations. As final step, the SiO y  may be oxidised to SiO 2  in an oxygen-containing gas at atmospheric pressure and temperatures of more than 200° C. or SiO y  may be converted to SiC at the surface of the plane-parallel structures in a carbon-containing gas at from 500° C. to 1500° C. The products produced in that manner are distinguished by high uniformity of thickness.

The present invention relates to methods of producing plane-parallelstructures of silicon suboxide, silicon dioxide and/or silicon carbide,to plane-parallel structures obtainable by such methods, and to the usethereof.

Silicon suboxide (SiO_(y)) is understood to mean combinations orcompounds of silicon with oxygen wherein the oxygen content is notsufficient for complete oxidation of the silicon. In the context of thepresent patent application, the expression silicon suboxide is intendedalso to encompass silicon monoxide (that is to say, SiO or SiO_(y)wherein y=1).

Plane-parallel structures of silicon dioxide are used as catalystsupports, it being possible to obtain a large active surface area ofcatalyst material to be applied chemically in accordance with knownmethods, whilst it has a low weight per unit area of typically from 0.1to 1.0 g/m². Further applications of such plane-parallel structures areto be found in the field of the surface coating industry, wherein it isdesired to incorporate colourless structures that have, as far aspossible, the same refractive index as the surface coating, in order toachieve an improvement in the resistance to abrasion of the surfacecoating layers. Further applications are low-ohm conductive surfacecoatings, in which case the plane-parallel structures are subjected tofurther coating with metals of high conductivity. They are also suitableas supports for further coatings.

The direct vapour-deposition of silicon dioxide onto surfaces by the PVDmethod is known. For that purpose, in almost all cases, vaporisation bymeans of an electron beam from water-cooled copper crucibles is used inorder to avoid a chemical reaction of the liquid silicon dioxide withcrucible material at the required vaporisation temperatures of from 1700to 1900° C. Examples thereof are to be found in U.S. Pat. No. 5,792,550,in the form of a double layer of aluminium oxide and silicon oxide forimproving packaging film barrier properties, and also in U.S. Pat. No.3,438,796. According to the latter specification, coloured structurescomprising a layered composite of aluminium and SiO₂ are produced bydirect vaporisation of SiO₂, the SiO₂ layers, according to Examples IIand III therein, being located as a protective layer on theair-interface surface. U.S. Pat. No. 6,150,022 also describes SiO₂protective layers on both sides of aluminium, the three-layer compositesubsequently being detached by dissolution and broken up into smallflakes. These are used in printing inks and surface coatings having ahigh reflecting power.

Transparent glass particles are sometimes used as an additive which isadmixed with surface coatings in order to increase their surfacehardness and resistance to abrasion. In accordance with U.S. Pat. No.4,985,380, a glass is obtained in molten form from a melted mixture ofsilicon dioxide, boron oxide and aluminium oxide. According to onemethod, which according to the patent specification is similar to thatof producing soap bubbles, thin-walled spheres of from 1 to 5 cm indiameter are blown therefrom. The spheres are then cooled, broken up andground and used as an additive in surface coatings. The laborious mannerof production and the uneven wall thickness of the resulting glassparticles of about 2 μm restrict such use.

U.S. Pat. No. 6,342,272 claims the use of powders comprising silicondioxide, glass, mica and other materials as a protective layer which isincorporated in synthetic resin coatings by thermal spraying. The methodrequires two layers of polymer and one layer of the inorganic materialsmentioned. It is not suitable for use over large areas.

The product ORMOCER®, produced by the known sol-gel method, consists ofinorganic-organic hybrid polymers which, according to information fromFraunhofer Silicafforschung, are also suitable for increasing theresistance to abrasion of surface coatings. They do not, however, formplane-parallel, purely inorganic structures but rather produce a networkof silicon alkoxides. The production process is discontinuous, and thethickness of the particles cannot be controlled.

A similar process according to U.S. Pat. No. 5,312,701 producesplane-parallel, ceramic structures in a wet method by means of thesolidification of a sol-gel consisting of boehmite, TEOS (an organicsilicon compound), boric acid and α-aluminium oxide. SiO₂-containingplane-parallel structures having a thickness in the range from 1 to 15μm are formed. Reference is made to their use as a filler forabrasion-resistant surface coatings. The method is lengthy. According toExample 8, stirring must be carried out for 3 days, followed byfreeze-drying and three hours of stoving at 1300° C. The process doesnot allow the thickness to be controlled precisely and it is not acontinuous process.

In accordance with U.S. Pat. No. 3,123,489 and U.S. Pat. No. 4,168,986,it is furthermore known that plane-parallel structures of smalldimensions can be produced by vapour-depositing first a salt layer ontoa carrier and, in the same vacuum, a product layer directly on top. Whenthe carrier is later brought into contact with water, the salt layerunderneath the product layer dissolves, the latter layer breaking upInto small plane-parallel structures. By further processing theresulting suspension, the plane-parallel structures can be isolated. Inthat method it is important that the plane-parallel structuresthemselves are not soluble in the solvent used.

Instead of salts, organic substances can also be vaporised. When theyare dissolved in an organic solvent, the product layer on top of thembreaks up into small, plane-parallel structures. Examples thereofinclude WO 00/62943 and U.S. Pat. No. 5,811,183. Such substances aremelamines, triazines, siliconised or fluorinated acrylic monomers.Similar organic monomers are described in U.S. Pat. No. 5,811,183 as aseparating agent layer capable of being vapour-deposited.

DE 4342574 and U.S. Pat. No. 5,239,611 describe the vaporisation ofsilicon monoxide in order to obtain barrier coatings on plastics films,as does W. Nassel: “Production, Properties, Processing and Applicationof SiO-coated Films” (Proceedings of 7^(th) International Conference onVacuum Web Coating” (ISBN 0-939997-15-0)). Silicon monoxide has theadvantage that it does not react, or reacts only slightly, with cruciblematerial of high-temperature metals, it is already vaporised at 1450° C.in vacuo in large amounts per unit time, and it is very readilyvaporised from resistance-heated sources. However, the intrinsic colourof such layers is the brownish-yellow colour typical of SiO, which isundesirable for many applications. The mechanical strength is lower thanthat of SiO₂.

A further method of producing plane-parallel SiO₂ structures, which doesnot require a PVD process, is described in EP 0 608 388 B1. A liquidfilm of waterglass is applied to an endless plastics belt, dried,treated with acid, dried again, mechanically separated from the belt,washed, and then baked. It is disadvantageous in that method that, incontrast to the invention described hereinbelow, the layer thickness ofproduct cannot, as it is in the case of the PVD method, be exactlycontrolled to a few nanometres. Furthermore, measures are requiredagainst the acid vapours that form, and the plastics belt must bereplaced relatively frequently because its surface becomes worn in theprocess.

It is likewise known from the prior art that vapour-deposited SiO layerscan be entirely converted to SiO₂ by heating in air at above 400° C.Such oxidative conversion is possible in the case of coated articlessuch as glass or ceramics, but not in the case of plastics.

A solution thereto is the generally known reactive vaporisation of SiOat about 10⁻² Pa with the simultaneous admission of oxygen into thevaporisation chamber. However, that is possible only with extremely slowvaporisation rates of a few milligrams per second, which are too low toproduce plane-parallel structures of SiO₂ on an industrial scale.

Calculation shows that, in the case of reactive vaporisation, oxidationof one mol of SiO to SiO₂ requires the introduction of at least 16 g ofoxygen (=½ mol), which corresponds to an amount of 11.2×10⁷ litres ofgas at 10⁻² Pa. With a vaporisation rate of at least 2.2 g of SiO (0.05mol) per second being necessary for the indicated purpose in order forit to be viable, that corresponds to the admission of at least 5.6million litres of oxygen gas per second at 10⁻² Pa. Because not everymolecule of oxygen will react with a molecule of SiO, the excess ofoxygen would have to be pumped off continuously. That exceeds thetechnical possibilities of even the largest PVD installations.

Because, for practical reasons, oxidation for the purpose of producingtransparent, colourless, plane-parallel SiO₂ structures cannot becarried out by thermal oxidation on the carrier itself or by reactivevaporisation of silicon suboxide in the presence of oxygen, according tothe invention thermal oxidation is postponed, as explained in detailhereinafter, until a later stage which is not dependent upon thetechnically possible vapour-deposition rate.

Setiowati and Kimura in “Silicon Carbide Powder Synthesis from SiliconMonoxide and Methane” (Journal of the American Ceramic Soc., Vol. 80 (3)1997, p. 757-760) describe the production of nano-powders and so-calledwhiskers of SiC from the reaction gases SiO and CH₄ at temperatures offrom 1400 to 1600° C. According to U.S. Pat. No. 5,618,510, carbonfibres are entirely converted into SiC fibres by reaction with SiOvapour at from 800 to 2000° C.

Neither method is suitable, however, for converting plane-parallelstructures of SiO, starting from their surfaces, at least partially intosilicon carbide.

The problem of the invention is to provide methods of producingplane-parallel structures of silicon suboxide, silicon dioxide and/orsilicon carbide resulting in plane-parallel structures havingthicknesses of from 20 to 2000 nm and length and width dimensions ofless than 0.2 mm, in industrial amounts, and with low outlay in terms ofequipment and also with good constancy of thickness.

The problem is solved by a method of producing plane-parallel structuresof SiO_(y), wherein 0.95≦y≦1.8, preferably wherein 1.1≦y≦1.8, especiallywherein 1.4≦y≦1.8, comprising the steps:

-   -   a) vapour-deposition of a separating agent onto a movable        carrier to produce a separating agent layer,    -   b) vapour-deposition of an SiO_(y) layer onto the separating        agent layer,    -   c) dissolution of the separating agent layer in a solvent,    -   d) separation of the SiO_(y) from the solvent,    -   the SiO_(y) layer in step b) being vapour-deposited from a        vaporiser containing a charge comprising a mixture of Si and        SiO₂, SiO_(y) or a mixture thereof, the weight ratio of Si to        SiO₂ being preferably in the range from 0.15:1 to 0.75:1, and        especially containing a stoichiometric mixture of Si and SiO₂,    -   and step c) being carried out at a pressure that is higher than        the pressure in steps a) and b) and lower than atmospheric        pressure, and    -   wherein plane-parallel structures of SiO_(y) obtainable by this        method have a thickness in the range preferably from 20 to 2000        nm, especially from 100 to 350 nm, the ratio of the thickness to        the surface area of the plane-parallel structures being        preferably less than 0.01 μm⁻¹. The plane-parallel structures        thereby produced are distinguished by high uniformity of        thickness.

The term “SiO_(y) with 0.95≦y≦1.80″ means that the molar ratio of oxygento silicon at the average value of the silicon oxide layer is from 0.95to 1.80. Accordingly, the term “SiO_(z) with 1.0<y<2.0” means that themolar ratio of oxygen to silicon at the average value of the siliconoxide layer is from 1.0 to 2.0. The composition of the silicon oxidelayer can be determined by ESCA (electron spectroscopy for chemicalanalysis).

The SiO_(y) layer in step b) is formed preferably from silicon monoxidevapour produced in the vaporiser by reaction of a mixture of Si and SiO₂at temperatures of more than 1300° C.

The vapour-deposition in steps a) and b) is carried out preferably undera vacuum of <0.5 Pa. The dissolution of the separating agent layer instep c) is carried out at a pressure in the range preferably from 1 to5×10⁴ Pa, especially from 600 to 10⁴ Pa, and more especially from 10³ to5×10³ Pa.

The separating agent vapour-deposited onto the carrier in step a) may bea lacquer (surface coating), a polymer, such as, for example, the(thermoplastic) polymers, in particular acryl- or styrene polymers ormixtures thereof, as described in U.S. Pat. No. 6,398,999, an organicsubstance soluble in organic solvents or water and vaporisable in vacuo,such as anthracene, anthraquinone, acetamidophenol, acetylsalicylicacid, camphoric anhydride, benzimidazole, benzene-1,2,4-tricarboxylicacid, biphenyl-2,2-dicarboxylic acid, bis(4-hydroxyphenyl)sulfone,dihydroxyanthraquinone, hydantoin, 3-hydroxybenzoic acid,8-hydroxyquinoline-5-sulfonic acid monohydrate, 4-hydroxycoumarin,7-hydroxycoumarin, 3-hydroxynaphthalene-2-carboxylic acid, isophthalicacid, 4,4-methylene-bis-3-hydroxynaphthalene-2-carboxylic acid,naphthalene-1,8-dicarboxylic anhydride, phthalimide and its potassiumsalt, phenolphthalein, phenothiazine, saccharin and its salts,tetraphenylmethane, triphenylene, triphenylmethanol or a mixture of atleast two of those substances. The separating agent is preferably aninorganic salt soluble in water and vaporisable in vacuo (see, forexample, DE 19844357), such as sodium chloride, potassium chloride,lithium chloride, sodium fluoride, potassium fluoride, lithium fluoride,calcium fluoride, sodium aluminium fluoride and disodium tetraborate.

The movable carrier may consist of one or more discs, cylinders or otherrotationally symmetrical bodies, which rotate about an axis (cf.WO01/25500), and consists preferably of one or more continuous metalbelts with or without a polymeric coating or of one or more polyimide orpolyethylene terephthalate belts (DE19844357).

A plurality of separating agent and SiO_(y) layers may preferably bevapour-deposited in alternating sequence, one after the other, onto themovable carrier in vacuo before they are removed by dissolution inaccordance with step c).

Step d) may comprise washing-out and subsequent filtration,sedimentation, centrifugation, decanting and/or evaporation. Theplane-parallel structures of SiO_(y) may, however, also be frozentogether with the solvent in step d) and subsequently subjected to aprocess of freeze-drying, whereupon the solvent is separated off as aresult of sublimation below the triple point and the dry SiO_(y) remainsbehind in the form of individual plane-parallel structures.

The plane-parallel structures of SiO_(y) separated off in step d) may beoxidised using an oxygen-containing gas such as, for example, air at atemperature of at least 200° C., especially at above 400° C., preferablyin the form of loose material, in a fluidised bed or by introductioninto an oxidising flame, preferably at a temperature in the range from500 to 1000° C., to form plane-parallel structures, and optionallysubjected to dipping, spraying or vapour treatment with at least oneorganic silane compound and/or at least one fluorine-containing organiccompound in order to obtain coupling properties with respect to otherorganic compounds or for the purpose of producing hydrophilic,hydrophobic or antistatic surfaces.

The invention relates also to plane-parallel structures of silicondioxide that are obtainable by this method and have a thicknesspreferably in the range from 20 to 2000 nm.

The plane-parallel structures of silicon dioxide or silicon suboxide maybe used, for example, in surface coatings or dispersion layers forincreasing the abrasion resistance and impact resistance of the surfacesof those surface coatings or dispersions.

Alternatively, the plane-parallel structures of SiO_(y) separated off inaccordance with step d) may, in a further step g), be treated with acarbon-containing gas selected from alkynes, for example acetylene,alkanes, for example methane, alkenes, aromatic compounds and mixturesthereof optionally in admixture with an oxygen containing compound, suchas, for example, aldehydes, ketones, water, carbon monoxide, carbondioxide or the like, or mixtures thereof, at from 500 to 1500° C.,preferably from 500 to 1000° C., preferably with the exclusion ofoxygen, where appropriate with an inert gas such as, for example, argonor helium being admixed with the carbon-containing gas. Preferably theoxygen-containing compound is contained in an amount of 0.01 to 10percent by volume based on the volume of carbon-containing gas andoxygen containing gas.

All of the SiO_(y) may be reacted to form SiC. Preferably from 5 to 90%by weight of the SiO_(y) are reacted to form SiC in the “carburisation”.

The residual amount of SiO_(y) of the plane-parallel structurescarburised in accordance with step g) may, in a further step h), beoxidised using an oxygen-containing gas, for example air, at atemperature of at least about 200° C. up to a maximum of about 400° C.

The plane-parallel structures obtained (carburised) in accordance withsteps g) and h), having a preferred thickness in the range from 20 to2000 nm, are novel and the invention relates also thereto. They may beused, for example, as corrosion-resistant additives having a Mohshardness of from 8 to 9 in coatings or as corrosion-resistant additivesin coating compositions in order to obtain properties of selectivereflection in the infra-red.

In accordance with an embodiment of the present invention, a salt, forexample NaCl, followed successively by a layer of silicon monoxide (SiO)is vapour-deposited onto a carrier, which may be a continuous metalbelt, passing by way of the vaporisers under a vacuum of <0.5 Pa. Thethicknesses of salt vapour-deposited are about 30 nm, those of the SiOfrom 20 to 2000 nm depending upon the intended purpose of the product.It must be borne in mind herein that, as a result of the heat ofcondensation and the radiant heat of the SiO vaporiser, considerableamounts of heat are transferred to the carrier. In contrast toconventional vapour-deposition of aluminium onto films in theroll-to-roll process, a reflector of infra-red, which as in the case ofaluminium reflects about 90% of the impinging heat radiation, is notformed in the case of SiO layers. On the contrary, in the case of avapour-deposited layer that is substantially transparent, some of theradiant heat is absorbed on its way through a transparent carrier film,it is then reflected at the cooling roller over which the film isrunning, and some of it is then again absorbed in the film.

Layer thicknesses of more than 100 nm result in substantial heating ofthe film carrier in the case of SiO vapour-deposition, which results insoftening and thermal degradation if the glass transition temperature ofthe plastics film is exceeded. It has therefore proved advantageous touse a metallic carrier which withstands such loading.

In accordance with the invention it is possible by that means to obtain,without thermally overloading the carrier, belt speeds that allow SiO tobe vapour-deposited in large amounts of SiO of several tonnes per month.Values of 10 kg per hour can be obtained when using vaporisers describedin DE 4342574 C1 and in U.S. Pat. No. 6,202,591.

Except under an ultra-high vacuum, in technical vacuums of a few 10⁻² Pavaporised SiO always condenses as SiO_(y) wherein 1≦y<1.8, especiallywherein 1.1<y<1.8, because high-vacuum apparatuses always contain, as aresult of gas emission from surfaces, traces of water vapour which reactwith the readily reactive SiO at vaporisation temperature.

On its further course, the belt-form carrier, which is closed to form aloop, runs through dynamic vacuum lock chambers of known mode ofconstruction (cf. U.S. Pat. No. 6,270,840) into a region of from 1 to5×10⁴ Pa pressure, preferably from 600 to 10⁴ Pa pressure, andespecially from 10³ to 5×10³ Pa pressure, where it is immersed in adissolution bath. The temperature of the solvent should be so selectedthat its vapour pressure is in the indicated pressure range. Withmechanical assistance, the separating agent layer rapidly dissolves andthe product layer breaks up into flakes, which are then present in thesolvent in the form of a suspension. On its further course, the belt isdried and freed from any contaminants still adhering to it. It runsthrough a second group of dynamic vacuum lock chambers back into thevaporisation chamber, where the process of coating with separating agentand product layer of SiO is repeated.

The suspension then present in both cases, comprising product structuresand solvent, and the separating agent dissolved therein, is thenseparated in a further operation In accordance with a known technique.For that purpose, the product structures are first concentrated in theliquid and rinsed several times with fresh solvent in order to wash outthe dissolved separating agent. The product, in the form of a solid thatis still wet, is then separated off by filtration, sedimentation,centrifugation, decanting or evaporation.

Then, after drying, the product can be subjected to oxidative heattreatment. Known methods are available for that purpose. Air or someother oxygen-containing gas is passed through the plane-parallelstructures of SiO_(y) wherein y is, depending on the vapour-depositionconditions, from 1 to about 1.8, which are in the form of loose materialor in a fluidised bed, at a temperature of more than 200° C., preferablymore than 400° C. and especially from 500 to 1000° C. After severalhours all the structures will have been oxidised to SiO₂. The productcan then be brought to the desired particle size by means of grinding orair-sieving and delivered for further use.

Alternatively thereto, the oxidation may be carried out in a hotoxidising gas stream, that is to say by means of blowing through anoxidative flame and collection in flight. It is also possible, however,to use any other method of oxidative heat treatment according to theknown art.

An economically useful side-effect of oxidation is that an increase inweight, which amounts to 36%, occurs on conversion from SiO to SiO₂.

In the production of plane-parallel structures of SiO₂, variants arepossible:

It is possible to arrange several separating agent and productvaporisers one after the other in the running direction of the belt inthe vaporisation zone. By that means there is obtained, with littleadditional outlay in terms of apparatus, a layer sequence of S+P+S+P,wherein S is the separating agent layer and P is the product layer. Ifthe number of vaporisers is doubled and the belt speed is the same,twice the amount of product is obtained.

Separating off the plane-parallel structures after washing-out atatmospheric pressure can be carried out under gentle conditions byfreezing the suspension, which has been concentrated to a solids contentof about 50%, and subjecting it in known manner to freeze-drying atabout −10° C. and 50 Pa pressure. The dry substance remains behind asproduct, which can be subjected to the steps of further processing bymeans of coating or chemical conversion.

Instead of using a continuous belt, it is possible to produce theproduct by carrying out the steps of vapour-deposition of separatingagent and SiO, of dissolution, and of drying the carrier, in anapparatus having a rotary body, in accordance with WO01/25500. Therotary body may be one or more discs, a cylinder or any otherrotationally symmetrical body.

The method known per se of producing silicon monoxide from silicon andsilicon dioxide by means of the reactionSi+SiO₂→2 SiOat more than 1300° C., preferably from 1300° C. to 1600° C., in vacuo,is combined in accordance with the invention with the vaporisation ofSiO. In vaporisers specifically set up for the purpose, a preferablystoichiometric mixture of fine silicon and quartz powder is heated to,for example, about 1450° C. under a high vacuum. The reaction product issilicon monoxide gas. Instead of collecting the silicon monoxide andgrinding it in order for it then to be vaporised at a later stage, thesilicon monoxide vapour resulting from the chemical reaction in vacuo isdirected directly onto the passing carrier, where it condenses as SiO.Separate production of SiO in a separate step is therefore notnecessary. It is also possible to use non-stoichiometric mixtures.However, residues of either SiO₂ or Si are left after the reaction. Whensuch non-stoichiometric mixtures having an excess of SiO₂ are used, itis advantageous that the excess remaining behind forms a solidprotective insulating layer against the wall of the vaporiser source.

In accordance with an embodiment of the invention, plane-parallelstructures of silicon dioxide in thicknesses of from 20 to 2000 nm areproduced by condensing, under a vacuum of <0.5 Pa, at least oneseparating agent and silicon suboxide (the latter produced from siliconmonoxide vapour formed simultaneously in the same vaporiser by reactionof silicon dioxide and silicon at temperatures of more than 1300° C.),one after the other, onto a movable carrier and, in the following step,removing them from the movable carrier by dissolution of the separatingagent, followed by separation from the solvent and, at a temperature ofmore than 200° C., oxidation in a heaped bed in the presence of oxygento form silicon dioxide.

In accordance with the invention, the vaporiser contains a chargecomprising a mixture of Si and SiO₂, SiO_(y), or a mixture thereof, theparticle size of the substances that react with one another (Si andSiO₂) being advantageously less than 0.3 mm. The weight ratio of Si toSiO₂ is advantageously in the range from 0.15:1 to 0.75:1 (parts byweight); preferably, a stoichiometric mixture is present. The amount ofSiO_(y) may be selected in accordance with practical requirements.SiO_(y) present in the vaporiser vaporises directly. Si and SiO₂ reactat a temperature of more than 1300° C. to form silicon monoxide vapour.The ratio of the thickness to the surface area of the plane-parallelstructures is preferably less than 0.01 μm⁻¹. The separating agentcondensed onto the carrier may be a water-soluble inorganic saltvaporisable in vacuo or a soluble organic substance vaporisable invacuo.

In accordance with the invention, step c) is carried out at a pressurethat is higher than the pressure in steps a) and b) and lower thanatmospheric pressure.

The movable carrier preferably comprises one or more continuous metalbelts, with or without a polymer coating, or one or more polyimide orpolyethylene terephthalate belts. The movable carrier may furthermorecomprise one or more discs, cylinders or other rotationally symmetricalbodies, which rotate about an axis.

In accordance with a preferred embodiment of the invention, a pluralityof separating agent layers and silicon suboxide layers in alternatingsuccession are vapour-deposited onto the movable carrier in vacuo,before being removed by dissolution of the condensed separating agentlayers. The plane-parallel structures of SiO_(y) are separated from theseparating agent solvent preferably by washing-out and subsequentfiltration, sedimentation, centrifugation, decanting or evaporation.Furthermore, the plane-parallel structures of silicon suboxide may,after washing-out of the dissolved separating agent contained in thesolvent, be frozen together with the solvent and subsequently subjectedto a process of freeze-drying, whereupon the solvent is separated off asa result of sublimation below the triple point and the dry siliconsuboxide remains behind in the form of individual plane-parallelstructures. The plane-parallel structures of silicon suboxide arepreferably oxidised to silicon dioxide at a temperature of more than200° C., preferably from 500 to 1000° C., in the presence of anoxygen-containing gas, which may also be air, in a heaped bed or in theform of loose material or in a fluidised bed. After the afore-mentionedoxidative treatment has been carried out, the plane-parallel structuresof silicon oxide may be subjected to further coating or surfacemodification by adding further substances in gaseous form to theoxygen-containing gas, the temperature being from 0° to 250° C.

The silicon suboxide condensed onto the movable carrier corresponds tothe formula SiO_(y) wherein 1≦y≦1.8, preferably wherein 1.1≦y≦1.5. It isalso possible, by using an excess of silicon in the vaporiser material,to obtain y values of less than 1, down to y=0.95.

In the production method described hereinbefore, further vaporisablesubstances such as organic pigments, especially metals or metal oxidesare preferably admixed with the silicon suboxide with the aim ofproviding the plane-parallel structures of silicon dioxide withoptically absorbing properties, it being possible for admixture to beeffected either In the solid phase or in the vapour phase by means ofvaporisation from a second source.

In the production method described hereinbefore, after oxidation hasbeen carried out, surface treatment of the produced plane-parallelstructures of silicon dioxide can be carried out by subjecting them todipping, spraying or vapour treatment with at least one organic silanecompound (such as, for example, a silane oligomer) and/or at least onefluorine-containing organic compound for the purpose of obtainingcoupling properties with respect to other organic compounds or forproducing hydrophilic, hydrophobic or antistatic surfaces. Theplane-parallel structures of silicon dioxide can be present in suspendedform in the surface coating or dispersion and, after the latter havedried, hard layers containing embedded structures oriented approximatelyparallel to the surface can be formed, which structures, in terms oftheir refractive index, differ by less than Δn=±0.2 from the refractiveindex of the surface coating or the dispersion and, at the same time,increase the abrasion resistance and impact resistance of the surface.It is possible, when producing surface coating or dispersion layers, forthe surface tension of the plane-parallel structures suspended thereinto be so modified by means of additives that they are orientedapproximately parallel at or near the surface. The surface tension ofthe plane-parallel structures may already have been modified beforeintroduction into the surface coating or dispersion by treating withsubstances in liquid or vapour form, which may be silane oligomers orfluorine-containing organic compounds, with the aim of causing theplane-parallel structures to be oriented approximately parallel at ornear the surface when the surface coating or dispersion dries.

Examples in accordance with the present invention are describedhereinbelow.

EXAMPLE I

In a vacuum system which in its fundamental points is constructedanalogously to U.S. Pat. No. 6,270,840, or as an alternative in a batchsystem, the following are vaporised, from vaporisers, in succession:sodium chloride (NaCl) as separating agent at about 900° C., and siliconmonoxide (SiO) as reaction product of Si and SiO₂ at from 1350 to 1550°C. The layer thickness of NaCl is typically 30-40 nm, that of SiO being,depending on the intended purpose of the end product, from 20 to 2000nm, in the present case 200 nm. The resistance-heated vaporisers are soconfigured in accordance with the known art that good uniformity isobtained over the working width. Vaporisation is carried out at about0.02 Pa, amounting to about 11 g of NaCl and 72 g of SiO per minute. Forsubsequently detaching the layers by dissolution of the separatingagent, the carrier on which vapour-depositon has taken place is sprayedat about 3000 Pa with delonised water and treated with mechanicalassistance using scrapers and with ultrasound. The NaCl enters solution,the SiO_(y) layer, which is insoluble, breaks up into flakes. Thesuspension is continuously removed from the dissolution chamber and, atatmospheric pressure, is concentrated by filtration and rinsed severaltimes with delonised water in order to remove Na⁺ and Cl⁻ ions that arepresent. That is followed by the steps of drying and (for the purpose ofoxidising SiO_(y) to SiO₂) heating the plane-parallel SiO_(y) structuresin the form of loose material at 700° C. for two hours in an oventhrough which air heated to 700° C. is passed. After cooling,comminution and grading by air-sieving are carried out. The product canbe delivered for further use.

EXAMPLE II

The steps of vapour-deposition and dissolution are the same as inExample I except that the vaporiser is filled with a mixture ofcommercially available silicon monoxide, silicon and silicon dioxide.That mixture is vaporised at about 1450° C., whereupon SiO that ispresent vaporises directly and the portions of Si and SiO₂simultaneously react to form SiO. The resulting vapour is directed ontothe passing carrier, where it condenses. After washing-out of the Na⁺and Cl⁻ ions, the solid is concentrated by means of filtration. Thefiltered material, which is still wet, containing about 25% residualwater, is frozen on a commercially available belt freezer at −5° C. inthe form of a layer 5 mm thick and is treated in a commerciallyavailable freeze-drying belt system. By virtue of the slow sublimationof the ice below the triple point of water, the SiO_(y) structures are,unlike in an evaporation method, not entrained and do not tend to formlumps. After a duration time of 2 hours they are discharged in dry form,they are oxidised to SiO₂ at 800° C. under air, and after cooling theyare delivered to the process of grinding and air-sieving.

The products produced in accordance with Examples I and II may also befurther treated at their surface in accordance with known methods inorder to obtain hydrophobic, hydrophilic or antistatic properties or toallow coupling of organic compounds. They may be further coated, forexample to form dye supports, catalyst supports or additives inabrasion-resistant surface-coatings. In the latter case, the productremains invisible even in a surface coating having the clarity of waterbecause the refractive indices are almost the same. The plane-parallelstructures become oriented parallel to the surface of the coated objectand, after subsequent treatment described hereinbelow, form a hard layersimilar to overlapping scales close to the surface of the surfacecoating, unlike the known additives of three-dimensional quartzparticles.

In order to achieve orientation of the plane-parallel structures ofsilicon dioxide approximately parallel to the surface of the surfacecoating layer(s), the surface tension of the structures can be modifiedby adding known chemicals to the surface coating, for example by meansof commercially available silane oligomers. Such oligomers, known underthe trade names DYNASILAN™, HYDROSIL™, PROTECTOSIL™ can also bedeposited directly onto the surface of the plane-parallel structures,either from a liquid phase or by condensation, before the latter areintroduced into the surface coating. Because such organic oligomers haveonly limited temperature resistance, it has proved advantageous to carryout such treatment only after oxidation to SiO₂ has taken place, attemperatures from 0° to 250° C.

The flakes of the present invention are not of a uniform shape.Nevertheless, for purposes of brevity, the flakes will be referred to ashaving a “diameter.” The SiO₂ flakes have a high plane-parallelism and adefined thickness in the range of ±10%, especially ±5% of the averagethickness. The SiO₂ flakes have a thickness of from 20 to 2000 nm,especially from 100 to 350 nm. It is presently preferred that thediameter of the flakes be in a preferred range of about 1-60 μm with amore preferred range of about 5-40 μm. Thus, the aspect ratio of theflakes of the present invention is in a preferred range of about 2.5-625with a more preferred range of about 50-250.

The SiO₂ flakes can be provided with one or more metal oxide and/ormetal layers, wherein in case of the metal oxide a metal oxide layerhaving a high index of refraction is deposited first. The metal oxidelayers can be applied by CVD (chemical vapour deposition) or by wetchemical coating, because the plane-parallel structures of SiO₂ can besubjected to thermal loading up to more than 1000° C. It being possible,where appropriate, for the metal oxides to be reduced (DE-A-19502231,WO97/39065, DE-A-19843014 and WO00/17277).

It is possible to obtain pigments that are more intense in colour andmore transparent by applying, on top of the TiO₂ layer, a metal oxide oflow refractive index, such as SiO₂, Al₂O₃, AlOOH, B₂O₃ or a mixturethereof, preferably SiO₂, and applying a further TiO₂ layer on top ofthe latter layer (EP-A-892832, EP-A-753545, WO93/08237, WO98/53011,WO9812266, WO9838254, WO99/20695, WO00/42111, and EP-A-1213330).

In the case of the wet chemical coating, the wet chemical coatingmethods developed for the production of pearlescent pigments may beused; these are described, for example, in DE-A-14 67468, DE-A-19 59988, DE-A-20 09 566, DE-A-22 14 545, DE-A-22 15 191, DE-A-22 44 298,DE-A-23 13 331, DE-A-25 22 572, DE-A-31 37 808, DE-A-31 37 809, DE-A-3151 343, DE-A-31 51 354, DE-A-31 51 355, DE-A-32 11 602 and DE-A-32 35017, DE 195 99 88, WO 93/08237, and WO 98/53001.

Pigments on the basis of SiO₂ substrates, comprising a metal oxide ofhigh index of refraction and optionally on top of the metal oxide ofhigh index of refraction a metal oxide of low index of refraction, or asemi-transparent metal layer are preferred.

Pigments on the basis of SiO₂ substrates, which have been coated by awet chemical method, in the indicated order are particularly preferred:

-   -   TiO₂ (substrate: SiO₂; layer: TiO₂), (SnO₂)TiO₂, Fe₂O₃,        Fe₂O₃.TiO₂ (substrate: SiO₂; mixed layer of Fe₂O₃ and TiO₂),        TiO₂/Fe₂O₃ (substrate: SiO₂; first layer: TiO₂; second layer:        Fe₂O₃), TiO₂/Berlin blau, TiO₂/Cr₂O₃, TiO₂/FeTiO₃,        TiO₂/SiO₂/TiO₂, (SnO₂)TiO₂/SiO₂/TiO₂, TiO₂/SiO₂/TiO₂/SiO₂/TiO₂        or TiO₂/SiO₂/Fe₂O₃.

Suitable metal oxide layers having a high index of refraction areespecially TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃, ZnO, or a mixture of thoseoxides, or an iron titanate, an iron oxide hydrate, a titanium suboxideor a mixture or mixed phase of those compounds. The coating with themetal oxide layer, especially TiO₂ layer, can be done by wet chemicalcoating as described in WO93/08237 or by CVD as described inDE-A-19614637.

It is furthermore possible to subject the finished pigment to subsequentcoating or subsequent treatment which further increases the light,weather and chemical stability or which facilitates handling of thepigment, especially its incorporation into various media. For example,the procedures described in DE-A-22 15 191, DE-A-31 51 354, DE-A-32 35017 or DE-A-33 34 598 are suitable as subsequent treatment or subsequentcoating. Instead of the metal oxide layer a semi-transparent metal layercan be used. Suitable metals are, for example, Cr, Ti, Mo, W, Al, Cu,Ag, Au, or Ni. Preferred pigments have the following layer structure:SiO₂ flakes+metal+SiO₂+metal oxide having a high index of refraction.

It is furthermore possible to convert plane-parallel structures ofSiO_(y), starting from their surface, partially to silicon carbide (SiC)(in the context of the present Application, this procedure shall bereferred to as “carburisation”). In similar manner to the oxidativeconversion of SiO_(y) structures to SiO₂ In accordance with theinvention, described in Example 1, it is possible to convertplane-parallel structures of SiO_(y) to SiC in a separate subsequentmethod. This is not a coating operation. This processing step results inmodified chemical and mechanical properties.

After partial conversion to SiC, the surface of the plane-parallelstructures is distinguished, in comparison to SiO₂, by greater hardness,reduced electrical insulation properties and reflection in the infra-redof up to 80% as opposed to reflection of 8% in the case of SiO₂structures. In accordance with the invention, the conversion is carriedout on all sides, that is to say even at the side edges of thestructures. Such a conversion makes use of the fact that SiO_(y) reactsat elevated temperature in the presence of carbon-containing gases toform SiC. The plane-parallel structures obtained by such means are noveland the present invention relates also thereto.

Consequently, the present invention relates also to plane-parallelstructures (pigments) based on plane-parallel SiO_(z) substrates havingon their surface a layer comprising silicon carbide (SiC), wherein0.95≦z≦2. The SiO_(y)-to-SiO₂ reaction takes place starting from thesurface of the plane-parallel structures and accordingly results in agradient rather than a sharp transition. This means that, in thatembodiment, the SiC-containing layer consists of (SiO_(y))_(a) and(SiC)_(b), wherein 0≦a<1 and 0<b≦1, with b being 1 and a being 0 closeto the surface of the pigment and the amount of SiC approaching 0 closeto the boundary with the SiO_(y) substrate. The SiO_(y) structures,which are from about 20 nm to about 2000 nm thick, are sufficientlyporous for such a reaction not to be limited only to the uppermost layerof SiO_(y) molecules.

The invention does not relate, however, to the production of material inpowder form in accordance with the prior art by means of the reaction oftwo gases, but rather to the partial or complete conversion of theplane-parallel structures of SiO_(y) produced in accordance with theinvention to silicon carbide (SiC), starting from their surfaces. It isfound, surprisingly, that in the case of plane-parallel structureshaving a thickness in the region of less than 2000 nm the conversion ofSiO_(y) to SiC already begins at relatively low temperatures, namelyfrom about 500° C.

For that purpose, the plane-parallel SiO_(y) structures obtained inExamples I and II, after they have been dried, are not further oxidisedusing an oxygen-containing gas as in Examples I and II but rather theyare caused to react in a gas-tight reactor heatable to a maximum ofabout 1500° C., preferably in the form of loose material, with acarbon-containing gas selected from alkynes, for example acetylene,alkanes, for example methane, alkenes, aromatic compounds or the like,and mixtures thereof optionally in admixture with an oxygen containingcompound, such as, for example, aldehydes, ketones, water, carbonmonoxide, carbon dioxide or the like, or mixtures thereof, at from 500to 1500° C., preferably from 500 to 1000° C., and advantageously withthe exclusion of oxygen. In order to temper the reaction, an inert gas,for example argon or helium, may be admixed with the carbon-containinggas.

At temperatures of less than about 500° C., that reaction generallyproceeds too slowly whereas temperatures of more than about 1500° C.necessitate expensive lining of the reaction vessel with inert materialssuch as SiC, carbon, graphite or composite materials thereof. Atpressures of less than about 1 Pa the reaction generally also proceedstoo slowly whereas, especially when the carbon-containing gases are lessreactive or are highly diluted with inert gas, it is perfectly possibleto operate at pressures of up to about 4000 bar, as are routinely used,for example, in HIP (“hot isostatic pressing”) systems.

In such carburisation, it is possible for all of the SiO_(y) to bereacted to form SiC; preferably from 5 to 90% by weight of the SiO_(y)are reacted to form SiC.

EXAMPLE III

The plane-parallel SiO_(y) structures produced in Example I are, afterdrying, heated in a gas-tight reactor, through which a mixture of argonand acetylene is being passed, to a temperature of 850° C. The workingpressure is 1 bar.

Step a:

A stream of argon gas at 900° C. is applied to an electrically heatedreactor having a volume of 2 litres and containing 20 g of loosematerial of previously dried plane-parallel SiO_(y) structures, preparedas in Example I, until all the loose material has reached thattemperature. Monomolecular layers of water adsorbed onto the loosematerial are desorbed as a result and carried away by the stream ofargon.

Step b:

As soon as the argon emerging from the loose material (which may, whereappropriate, be agitated) exhibits a temperature drop of less than 10°C. with respect to the hot gas entering, 5% by volume of acetylene isadmixed with the argon, the temperature being maintained at 850° C. Thegas is introduced at a number of places in the loose material and issupplied by means of a manifold comprising INCONEL™ tubes having aninternal diameter of 2 mm. The mass flow of acetylene is 1 mol per hour.

Step c:

After a treatment time of 2 hours, which has been found by experiment inpreliminary trials to be advantageous, the acetylene gas stream is shutdown and, with the heating switched off, subsequent flushing with pureargon is carried out for 10 minutes more until the gas outlettemperature has dropped to below 500° C. The obtained product showed asurface resistivity of less than 50000 ohm per square. It is assumedthat the surface conductivity is caused by an extremely thin carbonlayer, as the flakes become non-conducting, if heated in air.

Step d (this Step is Optional):

The argon supply is replaced by a supply of air at 400° C., withcontrolled heating, which is maintained over 15 minutes. The residualSiO_(y) in the plane-parallel structures oxidises to SiO₂. After afurther 15 minutes, cool air at room temperature is passed through theloose material. After a further 15 minutes, the product can be removedat approximately room temperature.

The temperature for the process of conversion of SiO_(y) to SiC is from500° to 1500° C., preferably from 500° C. to 1000° C., with a processduration of from about one hour to about twenty hours. The reactiontakes place starting from the surface of the plane-parallel structuresand accordingly results in a gradient rather than a sharp transition.The SiO_(y) structures, which are from about 20 nm to about 2000 nmthick, are sufficiently porous for such a reaction not to be limitedonly to the uppermost layer of SiO_(y) molecules.

The parameters of temperature, duration time and gas flow can be variedwithin wide limits and result in different degrees of conversion anddifferent conversion profiles, by which means it is possible toinfluence the properties of the product.

After carbide formation has been terminated, it is possible, optionally,for residual SiO_(y) still present in the plane-parallel structures tobe converted into SiO₂ by oxidation with an oxygen-containing gas,without destroying the SiC formed. Because of the large specific surfacearea of the plane-parallel structures, temperatures of about 400° C.should not, in this case, be exceeded in the presence of oxygen, incontrast to structures entirely of SiC, which can be used in air up toabout 1300° C. and in which the protective layer of SiO₂ that is formed,which is about 1000 nm thick, prevents further oxidation. The thicknessof the structures produced in accordance with the invention is, however,from 20 to 2000 nm, preferably, from 100 to 350 nm for mostapplications. Complete conversion of SiC into SiO₂ would be theconsequence if an excessively high oxidation temperature were to beused.

The product obtained by means of such conversion reflects up to about80% in the infra-red range of >10 μm, analogously to the disclosure ofhttp://www.cvdmaterials.com (Rohm & Haas). Therefore, in itstransparency, the product has the properties of an approximatelymonochromatic filter. Such products are especially suitable incombination with surface coatings for paints for reducing thermalemission at room temperature. In contrast to metals, such products arevery corrosion-resistant. The invention relates also to the use ofcorrosion-resistant additives which selectively reflect in the infra-redrange.

It is a substantial advantage of the product that, by virtue of suchconversion of SiO_(y) to SiC at the surfaces of the plane-parallelstructures, it is possible to obtain at those surfaces differentchemical, mechanical and infra-red properties. The surfaces converted toSiC facilitate further processing of such plane-parallel structures.Depending on their thickness, the latter have specific surface areas ofup to 20 m²/g and, in contrast to SiO₂ structures, require less in theway of measures protecting against inhalation when the solid material isfurther processed and used.

By virtue of the fact that the longer the reaction time and the higherthe temperature in the reactor the thicker the outer SiC zones become atthe expense of the inner SiO_(y) zone, the surface properties may bevaried in convenient manner. The SiC/SiO_(y) transitions are continuousso that they consist of zones rather than layers.

Such zones function as a multi-layer structure, although only a singlelayer, namely the SiO_(y) layer, has been produced by vapour-depositionin vacuo and the external zones of the plane-parallel structures havemerely been converted to SiC in an uncomplicated process outside thevacuum apparatus.

Such plane-parallel structures are novel and the present inventionrelates also thereto. The same is also true of the methods for theirpreparation. Such plane-parallel structures are suitable as additives totransparent or semi-transparent surface coatings or dispersions; theyare heat- and UV-resistant and, unlike aluminium structures, do notreact with water in ‘water-based’ surface coatings, which are nowgaining importance for ecological reasons.

Because the SiO₂/SiC pigment according to the invention has hightransparency in visible light and high reflectivity in the IR range,especially NIR range, it is suitable for use in the following areas:

-   -   (a) retro-reflective films, which are described, for example, in        WO 97/42261 and U.S. Pat. No. 5,387,458;    -   (b) solar-energy-controlling films of various construction,        which are described, for example, in GB 2 012 668; EP-A-355 962        and U.S. Pat. Nos. 3,290,203; 3,681,179; 3,776,805 and        4,095,013;    -   (c) corrosion-resistant silvered mirrors and solar reflectors,        which are described, for example, in U.S. Pat. No. 4,645,714;    -   (d) labels with reflective printing, which are described, for        example, in U.S. Pat. No. 5,564,843;    -   (e) UV-absorbing glass and glass coatings, which are described,        for example, in U.S. Pat. Nos. 5,372,889; 5,426,204; 5,683,804        and 5,618,626;    -   (f) agricultural films for keeping off the IR radiation of the        sun, so preventing excessive heating of, for example, a        greenhouse;    -   (g) films/glazes, which are described, for example, in WO        92/01557; JP 75-33286; 93-143668; 95-3217 and 96-143831; and        U.S. Pat. No. 5,643,676;    -   (h) windscreens and intermediate layers, which are described,        for example, in JP 80-40018; 90-192118; 90-335037; 90-335038;        92-110128 and 94-127591; and U.S. Pat. No. 5,618,863;    -   (i) optical films, which are described, for example, in WO        97/32225; and U.S. Pat. Nos. 4,871,784 and 5,217,794; and    -   (j) films, which reduce or change the emitted infrared (IR)        energy of military systems, to reduce their susceptibility to IR        sensors and/or IR guided weapons, which are described, for        example, in U.S. Pat. No. 5,814,367.

The above described process can also be used to produce plane-parallelpigments comprising at least one SiO_(z) layer, which comprises, on thetop surface, but not on the bottom surface, and on the side surfaces ofthe SiO_(z) layer, a layer comprising silicon carbide (SiC), wherein0.95≦z≦2. Such pigments can be produced, for example by PVD of a threelayer structure, SiOy/substrate/SiOy and then heating of the three layerstructure in a carbon containing gas, wherein the substrate is, forexample, transition metals having a melting point greater than 1000° C.,like Mo, Nb, Zr, Ti, Hf and W.

If, in the conversion described hereinbefore, a gas containing bothcarbon and nitrogen, for example ammonia, nitrogen, a primary, secondaryor tertiary amine, is used instead of a carbon-containing gas, there isobtained a pigment whose SiC-containing layer consists of (SiO_(y))_(a),(SiC)_(b) and (Si₃N₄)_(c), wherein 0<a<1, 0<b<1 and 0<c<1, with a being0 close to the surface of the pigment and with the amounts of SiC andSi₃N₄ approaching 0 close to the boundary with the SiO_(y) substrate. Itis possible for all of the SiO_(y) to be reacted to form Si₃N₄/SiC;preferably, from 5 to 90% by weight of the SiO_(y) are reacted to formSi₃N₄/SiC.

The parameters of temperature, duration time and gas flow can be variedwithin wide limits and result in different degrees of conversion anddifferent conversion profiles, by which means it is possible toinfluence the properties of the product.

After carbide formation and nitride formation have been terminated, itis possible, optionally, for residual SiO_(y) still present in theplane-parallel structures to be converted into SiO₂ by oxidation with anoxygen-containing gas, without destroying the Si₃N₄/SiC formed. Becauseof the large specific surface area of the plane-parallel structures,temperatures of about 400° C. should not, in this case, be exceeded inthe presence of oxygen.

It is also possible partially to convert the substrates of SiO_(y),starting from their surfaces, into silicon nitride (Si₃N₄). Afterpartial conversion to Si₃N₄, the surface of the SiO_(y) structures isdistinguished, in comparison to SiO₂, by greater hardness, highstrength, outstanding resistance to wear and very good chemicalresistance. In accordance with the invention, the conversion is carriedout on all sides, that is to say even at the side edges of thestructures. Such a conversion makes use of the fact that SiO_(y) reactsat elevated temperature in the presence of nitrogen-containing gases toform Si₃N₄.

For that purpose, after they have been dried, the plane-parallel SiO_(y)structures are caused to react in a gas-tight reactor heatable to amaximum of about 1500° C., preferably in the form of loose material,with a nitrogen-containing gas, for example ammonia, nitrogen or amixture thereof, at from 500 to 1500° C., preferably from 500 to 1000°C., and advantageously with the exclusion of oxygen. In order to temperthe reaction, an inert gas, for example argon or helium, may be admixedwith the nitrogen-containing gas.

It is possible for all of the SiO_(y) to be reacted to form Si₃N₄;preferably, from 5 to 90% by weight of the SiO_(y) are reacted to formSi₃N₄. The temperature for the process of conversion from SiO_(y) toSi₃N₄ is from 500° to 1500° C., preferably from 500° C. to 1000° C. Thereaction takes place starting from the surface of the plane-parallelstructures and accordingly results in a gradient rather than a sharptransition. This means that, in this embodiment, the Si₃N₄-containinglayer consists of (SiO_(y))_(a) and (Si₃N₄)_(d), wherein 0≦a<1 and0<d≦1, with d being 1 and a being 0 close to the surface of the pigmentand the amount of Si₃N₄ approaching 0 close to the boundary with theSiO_(y) substrate.

The parameters of temperature, duration time and gas flow can be variedwithin wide limits and result in different degrees of conversion anddifferent conversion profiles, by which means it is possible toinfluence the properties of the product.

After nitride formation has been terminated, it is possible, optionally,for residual SiO_(y) still present in the plane-parallel structures tobe converted into SiO₂ by oxidation with an oxygen-containing gas.Because of the large specific surface area of the plane-parallelstructures, temperatures of about 400° C. should not, in this case, beexceeded in the presence of oxygen.

The present invention relates furthermore to novel (plane-parallel)pigments based on SiO_(z) substrates in platelet form having, on thesurface of the SiO_(z) substrates, a layer comprising silicon carbide(SiC). The pigments are highly shear-stable and, in plastics, surfacecoatings or printing inks, result in high degrees of saturation andexcellent fastness properties and also, in the case of interferencepigments, a high degree of goniochromicity.

The pigment particles generally have a length of from 2 μm to 5 mm, awidth of from 2 μm to 2 mm, and a thickness of from 20 nm to 1.5 μm, anda ratio of length to thickness of at least 2:1, the particles having acore of SiO_(z) having two substantially parallel faces, the distancebetween which is the shortest axis of the core, and having anSiC-containing layer applied to the entire surface of the core and,optionally, further layers.

In order to obtain pigments having intense colours, further layers maybe applied to the SiC and/or Si₃N₄ layer of the pigments describedhereinbefore.

In a further embodiment, the pigment comprises a further layer of adielectric material having a “high” refractive index, that is to say arefractive index greater than about 1.65, which is applied to the entiresurface of the SiC-containing layer. Examples of such a dielectricmaterial are zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide(ZrO₂), titanium dioxide (TiO₂), carbon, indium oxide (In₂O₃), indiumtin oxide (ITO), tantalum pentoxide (Ta₂O₅), cerium oxide (CeO₂),yttrium oxide (Y₂O₃), europium oxide (Eu₂O₃), iron oxides such asiron(II)/iron(III) oxide (Fe₃O₄) and iron(III) oxide (Fe₂O₃), hafniumnitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO₂), lanthanumoxide (La₂O₃), magnesium oxide (MgO), neodymium oxide (Nd₂O₃),praseodymium oxide (Pr₆O₁₁), samarium oxide (Sm₂O₃), antimony trioxide(Sb₂O₃), silicon monoxides (SiO), selenium trioxide (Se₂O₃), tin oxide(SnO₂), tungsten trioxide (WO₃) or combinations thereof. The dielectricmaterial is preferably a metal oxide, it being possible for the metaloxide to be a single oxide or a mixture of oxides, with or withoutabsorbing properties, for example TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃ orZnO, with TiO₂ being especially preferred.

In this embodiment the thickness of the SiO_(z) layer is generally from20 to 1000 nm, preferably from 50 to 500 nm, that of the SiC layer from1 to 500 nm, preferably from 10 to 50 nm, and that of the TiO₂ layergenerally from 1 to 100 nm, preferably from 5 to 50 nm.

Additional coatings may be applied in a manner known per se for thepurpose of stabilisation with respect to weather and light.

The metal oxide layers can be applied by CVD (chemical vapourdeposition) or by wet chemical coating. The metal oxide layers can beobtained by decomposition of metal carbonyls in the presence of watervapour (relatively low molecular weight metal oxides such as magnetite)or in the presence of oxygen and, where appropriate, water vapour (e.g.nickel oxide and cobalt oxide). The metal oxide layers are especiallyapplied by means of oxidative gaseous phase decomposition of metalcarbonyls (e.g. iron pentacarbonyl, chromium hexacarbonyl; EP-A-45 851),by means of hydrolytic gaseous phase decomposition of metal alcoholates(e.g. titanium and zirconium tetra-n- and -iso-propanolate; DE-A-41 40900) or of metal halides (e.g. titanium tetrachloride; EP-A-338 428), bymeans of oxidative decomposition of organyl tin compounds (especiallyalkyl tin compounds such as tetrabutyltin and tetramethyltin; DE-A-44 03678) or by means of the gaseous phase hydrolysis of organyl siliconcompounds (especially di-tert-butoxyacetoxysilane) described in EP-A-668329, it being possible for the coating operation to be carried out in afluidised-bed reactor (EP-A-045 851 and EP-A-106 235). Al₂O₃ layers (B)can advantageously be obtained by controlled oxidation during thecooling of aluminium-coated pigments, which is otherwise carried outunder inert gas (DE-A-195 16 181).

Phosphate-, chromate- and/or vanadate-containing and also phosphate- andSiO₂-containing metal oxide layers can be applied in accordance with thepassivation methods described in DE-A-42 36 332 and in EP-A-678 561 bymeans of hydrolytic or oxidative gaseous phase decomposition ofoxide-halides of the metals (e.g. CrO₂Cl₂, VOCl₃), especially ofphosphorus oxyhalides (e.g. POCl₃), phosphoric and phosphorous acidesters (e.g. di- and tri-methyl and di- and tri-ethyl phosphite) and ofamino-group-containing organyl silicon compounds (e.g.3-aminopropyl-triethoxy- and -trimethoxy-silane.

Layers of oxides of the metals zirconium, titanium, iron and zinc, oxidehydrates of those metals, iron titanates, titanium suboxides or mixturesthereof are preferably applied by precipitation by a wet chemicalmethod, it being possible, where appropriate, for the metal oxides to bereduced. In the case of the wet chemical coating, the wet chemicalcoating methods developed for the production of pearlescent pigments maybe used; these are described, for example, in DE-A-1 4 67 468, DE-A-1 959 988, DE-A-20 09 566, DE-A-22 14 545, DE-A-22 15 191, DE-A-22 44 298,DE-A-23 13 331, DE-A-25 22 572, DE-A-31 37 808, DE-A-31 37 809, DE-A-3151 343, DE-A-31 51 354, DE-A-31 51 355, DE-A-32 11 602 and DE-A-32 35017.

For the purpose of coating, the substrate particles are suspended inwater and one or more hydrolysable metal salts are added at a pHsuitable for the hydrolysis, which is so selected that the metal oxidesor metal oxide hydrates are precipitated directly onto the particleswithout subsidiary precipitation occurring. The pH is usually keptconstant by simultaneously metering in a base. The pigments are thenseparated off, washed, dried and, where appropriate, baked, it beingpossible to optimise the baking temperature with respect to the coatingin question. If desired, after individual coatings have been applied,the pigments can be separated off, dried and, where appropriate, baked,and then again re-suspended for the purpose of precipitating furtherlayers.

The metal oxide layers are obtainable, for example, in analogy to amethod described in DE-A-1 95 01 307, by producing the metal oxide layerby controlled hydrolysis of one or more metal acid esters, whereappropriate in the presence of an organic solvent and a basic catalyst,by means of a sol-gel process. Suitable basic catalysts are, forexample, amines, such as triethylamine, ethylenediamine, tributylamine,dimethylethanolamine and methoxypropylamine. The organic solvent is awater-miscible organic solvent such as a C₁₋₄alcohol, especiallyisopropanol.

Suitable metal acid esters are selected from alkyl and aryl alcoholates,carboxylates, and carboxyl-radical- or alkyl-radical- oraryl-radical-substituted alkyl alcoholates or carboxylates of vanadium,titanium, zirconium, silicon, aluminium and boron. The use oftriisopropyl aluminate, tetraisopropyl titanate, tetraisopropylzirconate, tetraethyl orthosilicate and triethyl borate is preferred. Inaddition, acetylacetonates and acetoacetylacetonates of theaforementioned metals may be used. Preferred examples of that type ofmetal acid ester are zirconium acetylacetonate, aluminiumacetylacetonate, titanium acetylacetonate and diisobutyloleylacetoacetylaluminate or diisopropyloleyl acetoacetylacetonate andmixtures of metal acid esters, for example Dynasil® (Hũls), a mixedaluminium/silicon metal acid ester.

As a metal oxide having a high refractive index, titanium dioxide ispreferably used, the method described in U.S. Pat. No. 3,553,001 beingused, in accordance with an embodiment of the present invention, forapplication of the titanium dioxide layers.

An aqueous titanium salt solution is slowly added to a suspension of thematerial being coated, which suspension has been heated to about 50-100°C., especially 70-80° C., and a substantially constant pH value of aboutfrom 0.5 to 5, especially about from 1.2 to 2.5, is maintained bysimultaneously metering in a base such as, for example, aqueous ammoniasolution or aqueous alkali metal hydroxide solution. As soon as thedesired layer thickness of precipitated TiO₂ has been achieved, theaddition of titanium salt solution and base is stopped.

This method, also referred to as a titration method, is distinguished bythe fact that an excess of titanium salt is avoided. That is achieved byfeeding in for hydrolysis, per unit time, only that amount which isnecessary for even coating with the hydrated TiO₂ and which can be takenup per unit time by the available surface of the particles being coated.In principle, the anatase form of TiO₂ forms on the surface of thestarting pigment. By adding small amounts of SnO₂, however, it ispossible to force the rutile structure to be formed. For example, asdescribed in WO 93/08237, tin dioxide can be deposited before titaniumdioxide precipitation and the product coated with titanium dioxide canbe calcined at from 800 to 900° C.

Where appropriate, an SiO₂ protective layer can be applied on top of thetitanium dioxide layer, for which the following method may be used: Asoda waterglass solution is metered in to a suspension of the materialbeing coated, which suspension has been heated to about 50-100° C.,especially 70-80° C. The pH is maintained at from 4 to 10, preferablyfrom 6.5 to 8.5, by simultaneously adding 10% hydrochloric acid. Afteraddition of the waterglass solution, stirring is carried out for 30minutes.

It is possible to obtain pigments that are more intense in colour andmore transparent by applying, on top of the TiO₂ layer, a metal oxide of“low” refractive index, that is to say a refractive index smaller thanabout 1.65, such as SiO₂, Al₂O₃, AlOOH, B₂O₃ or a mixture thereof,preferably SiO₂, and applying a further TiO₂ layer on top of the latterlayer.

It is, in addition, possible to modify the powder colour of the pigmentby applying further layers such as, for example, coloured metal oxidesor Berlin Blue, compounds of transition metals, e.g. Fe, Cu, Ni, Co, Cr,or organic compounds such as dyes or colour lakes.

It is furthermore possible to subject the finished pigment to subsequentcoating or subsequent treatment which further increases the light,weather and chemical stability or which facilitates handling of thepigment, especially its incorporation into various media. For example,the procedures described in DE-A-22 15 191, DE-A-31 51 354, DE-A-32 35017 or DE-A-33 34 598 are suitable as subsequent treatment or subsequentcoating.

In addition, the pigment according to the invention can also be coatedwith poorly soluble, firmly adhering, inorganic or organic colourants.Preference is given to the use of colour lakes and, especially,aluminium colour lakes. For that purpose an aluminium hydroxide layer isprecipitated, which is, in a second step, laked by using a colour lake(DE-A-24 29 762 and DE 29 28 287).

Furthermore, the pigment according to the invention may also have anadditional coating with complex salt pigments, especially cyanoferratecomplexes (EP-A-141 173 and DE-A-23 13 332).

The pigments according to the invention are very shear-stable, resultingfrom the fact that in the method of the invention a very good bond isobtained between SiO₂, SiC and SiN layers and the layers of dielectricmaterial.

The pigments according to the invention can be used for all customarypurposes, for example for colouring polymers in the mass, surfacecoatings (including effect finishes, including those for the automotivesector) and printing inks, and also, for example, for applications incosmetics. Such applications are known from reference works, for example“Industrielle Organische Pigmente” (W. Herbst and K. Hunger, VCHVerlagsgesellschaft mbH, Weinheim/New York, 2nd, completely revisededition, 1995).

When the pigments according to the invention are interference pigments(effect pigments), they are goniochromatic and result in brilliant,highly saturated (lustrous) colours. They are accordingly veryespecially suitable for combination with conventional, transparentpigments, for example organic pigments such as, for example,diketopyrrolopyrroles, quinacridones, dioxazines, perylenes,isoindolinones etc., it being possible for the transparent pigment tohave a similar colour to the effect pigment. Especially interestingcombination effects are obtained, however, in analogy to, for example,EP 388 932 or EP 402 943, when the colour of the transparent pigment andthat of the effect pigment are complementary.

The pigments according to the invention can be used with excellentresults for pigmenting high molecular weight organic material.

The high molecular weight organic material for the pigmenting of whichthe pigments or pigment compositions according to the invention may beused may be of natural or synthetic origin. High molecular weightorganic materials usually have molecular weights of about from 10³ to10⁸ g/mol or even more. They may be, for example, natural resins, dryingoils, rubber or casein, or natural substances derived therefrom, such aschlorinated rubber, oil-modified alkyd resins, viscose, cellulose ethersor esters, such as ethylcellulose, cellulose acetate, cellulosepropionate, cellulose acetobutyrate or nitrocellulose, but especiallytotally synthetic organic polymers (thermosetting plastics andthermoplastics), as are obtained by polymerisation, polycondensation orpolyaddition. From the class of the polymerisation resins there may bementioned, especially, polyolefins, such as polyethylene, polypropyleneor polyisobutylene, and also substituted polyolefins, such aspolymerisation products of vinyl chloride, vinyl acetate, styrene,acrylonitrile, acrylic acid esters, methacrylic acid esters orbutadiene, and also copolymerisation products of the said monomers, suchas especially ABS or EVA.

From the series of the polyaddition resins and polycondensation resinsthere may be mentioned, for example, condensation products offormaldehyde with phenols, so-called phenoplasts, and condensationproducts of formaldehyde with urea, thiourea or melamine, so-calledaminoplasts, and the polyesters used as surface-coating resins, eithersaturated, such as alkyd resins, or unsaturated, such as maleate resins;also linear polyesters and polyamides, polyurethanes or silicones.

The said high molecular weight compounds may be present singly or inmixtures, in the form of plastic masses or melts. They may also bepresent in the form of their monomers or In the polymerised state indissolved form as film-formers or binders for surface coatings orprinting inks, such as, for example, boiled linseed oil, nitrocellulose,alkyd resins, melamine resins and urea-formaldehyde resins or acrylicresins.

Depending on the intended purpose, it has proved advantageous to use theeffect pigments or effect pigment compositions according to theinvention as toners or in the form of preparations. Depending on theconditioning method or intended application, it may be advantageous toadd certain amounts of texture-improving agents to the effect pigmentbefore or after the conditioning process, provided that this has noadverse effect on use of the effect pigments for colouring highmolecular weight organic materials, especially polyethylene. Suitableagents are, especially, fatty acids containing at least 18 carbon atoms,for example stearic or behenic acid, or amides or metal salts thereof,especially magnesium salts, and also plasticisers, waxes, resin acids,such as abietic acid, rosin soap, alkylphenols or aliphatic alcohols,such as stearyl alcohol, or aliphatic 1,2-dihydroxy compounds containingfrom 8 to 22 carbon atoms, such as 1,2-dodecanediol, and also modifiedcolophonium maleate resins or fumaric acid colophonium resins. Thetexture-improving agents are added in amounts of preferably from 0.1 to30% by weight, especially from 2 to 15% by weight, based on the endproduct.

The (effect) pigments according to the invention can be added in anytinctorially effective amount to the high molecular weight organicmaterial being pigmented. A pigmented substance composition comprising ahigh molecular weight organic material and from 0.01 to 80% by weight,preferably from 0.1 to 30% by weight, based on the high molecular weightorganic material, of an pigment according to the invention isadvantageous. Concentrations of from 1 to 20% by weight, especially ofabout 10% by weight, can often be used in practice.

High concentrations, for example those above 30% by weight, are usuallyin the form of concentrates (“masterbatches”) which can be used ascolorants for producing pigmented materials having a relatively lowpigment content, the pigments according to the invention having anextraordinarily low viscosity in customary formulations so that they canstill be processed well.

For the purpose of pigmenting organic materials, the effect pigmentsaccording to the invention may be used singly. It is, however, alsopossible, in order to achieve different hues or colour effects, to addany desired amounts of other colour-imparting constituents, such aswhite, coloured, black or effect pigments, to the high molecular weightorganic substances in addition to the effect pigments according to theinvention. When coloured pigments are used in admixture with the effectpigments according to the invention, the total amount is preferably from0.1 to 10% by weight, based on the high molecular weight organicmaterial. Especially high goniochromicity is provided by the preferredcombination of an effect pigment according to the invention with acoloured pigment of another colour, especially of a complementarycolour, with colorations made using the effect pigment and colorationsmade using the coloured pigment having, at a measurement angle of 10°, adifference in hue (ΔH^(⋆)) of from 20 to 340, especially from 150 to210.

Preferably, the effect pigments according to the invention are combinedwith transparent coloured pigments, it being possible for thetransparent coloured pigments to be present either in the same medium asthe effect pigments according to the invention or in a neighbouringmedium. An example of an arrangement in which the effect pigment and thecoloured pigment are advantageously present in neighbouring media is amulti-layer effect surface coating.

The pigmenting of high molecular weight organic substances with thepigments according to the invention is carried out, for example, byadmixing such a pigment, where appropriate in the form of a masterbatch,with the substrates using roll mills or mixing or grinding apparatuses.The pigmented material is then brought into the desired final form usingmethods known per se, such as calendering, compression moulding,extrusion, coating, pouring or injection moulding. Any additivescustomary in the plastics industry, such as plasticisers, fillers orstabilisers, can be added to the polymer, in customary amounts, beforeor after incorporation of the pigment. In particular, in order toproduce non-rigid shaped articles or to reduce their brittleness, it isdesirable to add plasticisers, for example esters of phosphoric acid,phthalic acid or sebacic acid, to the high molecular weight compoundsprior to shaping.

For pigmenting surface coatings and printing inks, the high molecularweight organic materials and the effect pigments according to theinvention, where appropriate together with customary additives such as,for example, fillers, other pigments, siccatives or plasticisers, arefinely dispersed or dissolved in the same organic solvent or solventmixture, it being possible for the individual components to be dissolvedor dispersed separately or for a number of components to be dissolved ordispersed together, and only thereafter for all the components to bebrought together.

Dispersing an effect pigment according to the invention in the highmolecular weight organic material being pigmented, and processing apigment composition according to the invention, are preferably carriedout subject to conditions under which only relatively weak shear forcesoccur so that the effect pigment is not broken up into smaller portions.

The colorations obtained, for example in plastics, surface coatings orprinting inks, especially in surface coatings or printing inks, moreespecially in surface coatings, are distinguished by excellentproperties, especially by extremely high saturation, outstandingfastness properties and high goniochromicity.

When the high molecular weight material being pigmented is a surfacecoating, it is especially a speciality surface coating, very especiallyan automotive finish.

The effect pigments according to the invention are also suitable formaking-up the lips or the skin and for colouring the hair or the nails.

The invention accordingly relates also to a cosmetic preparation orformulation comprising from 0.0001 to 90% by weight of a pigment,especially an effect pigment, according to the invention and from 10 to99.9999% of a cosmetically suitable carrier material, based on the totalweight of the cosmetic preparation or formulation.

Such cosmetic preparations or formulations are, for example, lipsticks,blushers, foundations, nail varnishes and hair shampoos.

The pigments may be used singly or in the form of mixtures. It is, inaddition, possible to use pigments according to the invention togetherwith other pigments and/or colorants, for example in combinations asdescribed hereinbefore or as known in cosmetic preparations.

The cosmetic preparations and formulations according to the inventionpreferably contain the pigment according to the invention in an amountfrom 0.005 to 50% by weight, based on the total weight of thepreparation.

Suitable carrier materials for the cosmetic preparations andformulations according to the invention include the customary materialsused in such compositions.

The cosmetic preparations and formulations according to the inventionmay be in the form of, for example, sticks, ointments, creams,emulsions, suspensions, dispersions, powders or solutions. They are, forexample, lipsticks, mascara preparations, blushers, eye-shadows,foundations, eyeliners, powder or nail varnishes.

If the preparations are in the form of sticks, for example lipsticks,eye-shadows, blushers or foundations, the preparations consist for aconsiderable part of fatty components, which may consist of one or morewaxes, for example ozokerite, lanolin, lanolin alcohol, hydrogenatedlanolin, acetylated lanolin, lanolin wax, beeswax, candelilla wax,microcrystalline wax, carnauba wax, cetyl alcohol, stearyl alcohol,cocoa butter, lanolin fatty acids, petrolatum, petroleum jelly, mono-,di- or tri-glycerides or fatty esters thereof that are solid at 25° C,silicone waxes, such as methyloctadecane-oxypolysiloxane andpoly(dimethylsiloxy)stearoxysiloxane, stearic acid monoethanolamine,colophane and derivatives thereof, such as glycol abietates and glycerolabietates, hydrogenated oils that are solid at 25° C., sugar glyceridesand oleates, myristates, lanolates, stearates and dihydroxystearates ofcalcium, magnesium, zirconium and aluminium.

The fatty component may also consist of a mixture of at least one waxand at least one oil, in which case the following oils, for example, aresuitable: paraffin oil, purcelline oil, perhydrosqualene, sweet almondoil, avocado oil, calophyllum oil, castor oil, sesame oil, jojoba oil,mineral oils having a boiling point of about from 310 to 410° C.,silicone oils, such as dimethylpolysiloxane, linoleyl alcohol, linolenylalcohol, oleyl alcohol, cereal grain oils, such as wheatgerm oil,isopropyl lanolate, isopropyl palmitate, isopropyl myristate, butylmyristate, cetyl myristate, hexadecyl stearate, butyl stearate, decyloleate, acetyl glycerides, octanoates and decanoates of alcohols andpolyalcohols, for example of glycol and glycerol, ricinoleates ofalcohols and polyalcohols, for example of cetyl alcohol, isostearylalcohol, isocetyl lanolate, isopropyl adipate, hexyl laurate and octyldodecanol.

The fatty components in such preparations in the form of sticks maygenerally constitute up to 99.91% by weight of the total weight of thepreparation.

The cosmetic preparations and formulations according to the inventionmay additionally comprise further constituents, such as, for example,glycols, polyethylene glycols, polypropylene glycols, monoalkanolamides,non-coloured polymeric, inorganic or organic fillers, preservatives, UVfilters or other adjuvants and additives customary In cosmetics, forexample a natural or synthetic or partially synthetic di- ortri-glyceride, a mineral oil, a silicone oil, a wax, a fatty alcohol, aGuerbet alcohol or ester thereof, a lipophilic functional cosmeticactive ingredient, including sun-protection filters, or a mixture ofsuch substances.

A lipophilic functional cosmetic active ingredient suitable for skincosmetics, an active ingredient composition or an active ingredientextract is an ingredient or a mixture of ingredients that is approvedfor dermal or topical application. The following may be mentioned by wayof example:

-   -   active ingredients having a cleansing action on the skin surface        and the hair; these include all substances that serve to cleanse        the skin, such as oils, soaps, synthetic detergents and solid        substances;    -   active ingredients having a deodorising and        perspiration-inhibiting action: they include antiperspirants        based on aluminium salts or zinc salts, deodorants comprising        bactericidal or bacteriostatic. deodorising substances, for        example triclosan, hexachlorophene, alcohols and cationic        substances, such as, for example, quaternary ammonium salts, and        odour absorbers, for example ®Grillocin (combination of zinc        ricinoleate and various additives) or triethyl citrate        (optionally in combination with an antioxidant, such as, for        example, butyl hydroxytoluene) or ion-exchange resins;    -   active ingredients that offer protection against sunlight (UV        filters): suitable active ingredients are filter substances        (sunscreens) that are able to absorb UV radiation from sunlight        and convert it into heat; depending on the desired action, the        following light-protection agents are preferred:        light-protection agents that selectively absorb sunburn-causing        high-energy UV radiation in the range of approximately from 280        to 315 nm (UV-B absorbers) and transmit the longer-wavelength        range of, for example, from 315 to 400 nm (UV-A range), as well        as light-protection agents that absorb only the        longer-wavelength radiation of the UV-A range of from 315 to 400        nm (UV-A absorbers);    -   suitable light-protection agents are, for example, organic UV        absorbers from the class of the p-aminobenzoic acid derivatives,        salicylic acid derivatives, benzophenone derivatives,        dibenzoylmethane derivatives, diphenyl acrylate derivatives,        benzofuran derivatives, polymeric UV absorbers comprising one or        more organosilicon radicals, cinnamic acid derivatives, camphor        derivatives, trianilino-s-triazine derivatives,        phenylbenzimidazolesulfonic acid and salts thereof, menthyl        anthranilates, benzotriazole derivatives, and/or an inorganic        micropigment selected from aluminium oxide- or silicon        dioxide-coated TiO₂, zinc oxide or mica;    -   active ingredients against insects (repellents) are agents that        are intended to prevent insects from touching the skin and        becoming active there; they drive insects away and evaporate        slowly; the most frequently used repellent is diethyl toluamide        (DEET); other common repellents will be found, for example, in        “Pflegekosmetik” (W. Raab and U. Kindl, Gustav-Fischer-Verlag        Stuttgart/New York,1991) on page 161;    -   active ingredients for protection against chemical and        mechanical influences: these include all substances that form a        barrier between the skin and external harmful substances, such        as, for example, paraffin oils, silicone oils, vegetable oils,        PCL products and lanolin for protection against aqueous        solutions, film-forming agents, such as sodium alginate,        triethanolamine alginate, polyacrylates, polyvinyl alcohol or        cellulose ethers for protection against the effect of organic        solvents, or substances based on mineral oils, vegetable oils or        silicone oils as “lubricants” for protection against severe        mechanical stresses on the skin;    -   moisturising substances: the following substances, for example,        are used as moisture-controlling agents (moisturisers): sodium        lactate, urea, alcohols, sorbitol, glycerol, propylene glycol,        collagen, elastin and hyaluronic acid;    -   active Ingredients having a keratoplastic effect: benzoyl        peroxide, retinoic acid, colloidal sulfur and resorcinol;    -   antimicrobial agents, such as, for example, triclosan or        quaternary ammonium compounds;    -   oily or oil-soluble vitamins or vitamin derivatives that can be        applied dermally: for example vitamin A (retinol in the form of        the free acid or derivatives thereof), panthenol, pantothenic        acid, folic acid, and combinations thereof, vitamin E        (tocopherol), vitamin F; essential fatty acids; or niacinamide        (nicotinic acid amide);    -   vitamin-based placenta extracts: active ingredient compositions        comprising especially vitamins A, C, E, B₁, B₂, B₆, B₁₂, folic        acid and biotin, amino acids and enzymes as well as compounds of        the trace elements magnesium, silicon, phosphorus, calcium,        manganese, iron or copper;    -   skin repair complexes: obtainable from inactivated and        disintegrated cultures of bacteria of the bifidus group;    -   plants and plant extracts: for example arnica, aloe, beard        lichen, ivy, stinging nettle, ginseng, henna, camomile,        marigold, rosemary, sage, horsetail or thyme;    -   animal extracts: for example royal jelly, propolis, proteins or        thymus extracts;    -   cosmetic oils that can be applied dermally: neutral oils of the        Miglyol 812 type, apricot kernel oil, avocado oil, babassu oil,        cottonseed oil, borage oil, thistle oil, groundnut oil,        gamma-oryzanol, rosehip-seed oil, hemp oil, hazelnut oil,        blackcurrant-seed oil, jojoba oil, cherry-stone oil, salmon oil,        linseed oil, cornseed oil, macadamia nut oil, almond oil,        evening primrose oil, mink oil, olive oil, pecan nut oil, peach        kernel oil, pistachio nut oil, rape oil, rice-seed oil, castor        oil, safflower oil, sesame oil, soybean oil, sunflower oil, tea        tree oil, grapeseed oil or wheatgerm oil.

The preparations in stick form are preferably anhydrous but may incertain cases comprise a certain amount of water which, however, ingeneral does not exceed 40% by weight, based on the total weight of thecosmetic preparation.

If the cosmetic preparations and formulations according to the inventionare in the form of semi-solid products, that is to say in the form ofointments or creams, they may likewise be anhydrous or aqueous. Suchpreparations and formulations are, for example, mascaras, eyeliners,foundations, blushers, eye-shadows, or compositions for treating ringsunder the eyes.

If, on the other hand, such ointments or creams are aqueous, they areespecially emulsions of the water-in-oil type or of the oil-in-watertype that comprise, apart from the pigment, from 1 to 98.8% by weight ofthe fatty phase, from 1 to 98.8% by weight of the aqueous phase and from0.2 to 30% by weight of an emulsifier.

Such ointments and creams may also comprise further conventionaladditives, such as, for example, perfumes, antoxidants, preservatives,gel-forming agents, UV filters, colorants, pigments, pearlescent agents,non-coloured polymers as well as inorganic or organic fillers.

If the preparations are in the form of a powder, they consistsubstantially of a mineral or inorganic or organic filler such as, forexample, talcum, kaolin, starch, polyethylene powder or polyamidepowder, as well as adjuvants such as binders, colorants etc.

Such preparations may likewise comprise various adjuvants conventionallyemployed in cosmetics, such as fragrances, antioxidants, preservativesetc.

If the cosmetic preparations and formulations according to the inventionare nail varnishes, they consist essentially of nitrocellulose and anatural or synthetic polymer in the form of a solution in a solventsystem, it being possible for the solution to comprise other adjuvants,for example pearlescent agents.

In that embodiment, the coloured polymer is present in an amount ofapproximately from 0.1 to 5% by weight.

The cosmetic preparations and formulations according to the inventionmay also be used for colouring the hair, in which case they are used Inthe form of shampoos, creams or gels that are composed of the basesubstances conventionally employed In the cosmetics industry and apigment according to the invention.

The cosmetic preparations and formulations according to the inventionare prepared in conventional manner, for example by mixing or stirringthe components together, optionally with heating so that the mixturesmelt.

The Examples that follow illustrate the invention without limiting thescope thereof.

EXAMPLE 1

In a vacuum system which in its fundamental points is constructedanalogously to the system described in U.S. Pat. No. 6,270,840, thefollowing are vaporised, from vaporisers, in succession: sodium chloride(NaCl) as separating agent at about 900° C., and silicon monoxide (SiO)as reaction product of Si and SiO₂ at from 1350 to 1550° C. The layerthickness of NaCl is typically 30-40 nm, that of SiO_(y) being,depending on the intended purpose of the end product, from 100 to 2000nm, in the present case 200 nm. Vaporisation is carried out at about0.02 Pa, amounting to about 11 g of NaCl and 72 g of SiO per minute. Forsubsequently detaching the layers by dissolution of the separatingagent, the carrier on which vapour-deposition has taken place is sprayedat about 3000 Pa with deionised water and treated with mechanicalassistance using scrapers and with ultrasound. The NaCl dissolves andthe SiO_(y) layer, which is insoluble, breaks up into flakes. Thesuspension is continuously removed from the dissolution chamber and, atatmospheric pressure, is concentrated by filtration and rinsed severaltimes with deionised water in order to remove Na⁺ and Cl⁻ ions that arepresent. That is followed by the steps of drying and (for the purpose ofoxidising SiO_(y) to SiO₂) heating the plane-parallel SiO_(y) structuresin the form of loose material at 700° C. for two hours in an oventhrough which air heated to 700° C. is passed. After cooling,comminution and grading by air-sieving are carried out. The product canbe delivered for further use.

EXAMPLE 2

The steps of vapour-deposition and dissolution are the same as inExample 1 except that the vaporiser is filled with a mixture ofcommercially available silicon monoxide, silicon and silicon dioxide.That mixture is vaporised at about 1450° C., whereupon SiO that ispresent vaporises directly and the portions of Si and SiO₂simultaneously react to form SiO. The resulting vapour is directed ontothe passing carrier, where it condenses. After washing-out of the Na⁺and Cl⁻ ions, the solid is concentrated by means of filtration. Thefiltered material, which is still wet, containing about 25% residualwater, is frozen on a commercially available belt freezer at −5° C. inthe form of a layer 5 mm thick and is treated in a commerciallyavailable freeze-drying belt system. By virtue of the slow sublimationof the ice below the triple point of water, the SiO_(y) structures are,unlike in an evaporation method, not entrained and do not tend to formlumps. After a duration time of 2 hours they emerge in dry form, theyare oxidised to SiO₂ at 800° C. under air, and after cooling they aredelivered to the process of grinding and air-sieving.

EXAMPLE 3

After drying, the plane-parallel SiO_(y) structures produced in Example1 are heated in a gas-tight reactor, through which a mixture of argonand acetylene is being passed, to a temperature of 850° C. The workingpressure is 1 bar:

A stream of argon gas at 900° C. is applied to an electrically heatedreactor having a volume of 2 litres and containing 20 g of loosematerial of previously dried plane-parallel, 350 nm thick SiO_(y)structures, prepared as in Example 1, until all the loose material hasreached that temperature. Monomolecular layers of water adsorbed ontothe loose material are desorbed as a result and carried away by thestream of argon.

As soon as the argon emerging from the loose material (which may, whereappropriate, be agitated) exhibits a temperature drop of less than 10°C. with respect to the hot gas entering, 10% by volume of acetylene isadmixed with the argon, the temperature being maintained at 800° C. Thegas is introduced at a number of places in the loose material and issupplied by means of a manifold comprising INCONEL™ tubes having aninternal diameter of 2 mm. After a treatment time of 2, 4 and 7 hours,which have been found by experiment in preliminary trials to beadvantageous, the acetylene gas stream is shut down and, with theheating switched off, subsequent flushing with pure argon is carried outfor 10 minutes more until the gas outlet temperature has dropped tobelow 500° C.

The argon supply is replaced by a supply of air at 400° C., withcontrolled heating, which is maintained over 15 minutes. The residualSiO_(y) in the plane-parallel structures oxidises to SiO₂. After afurther 15 minutes, cool air at room temperature is passed through theloose material. After a further 15 minutes, the product can be removedat approximately room temperature.

In dependence upon the treatment time, different colours (reflectanceand transmittance) are obtained: Colour Colour Example Treatment time(reflectance) (transmittance) 3a 2 blue yellow 3b 4 green reddish 3c 7yellow blue

EXAMPLE 4

a) The Pigments Obtained in Examples 3a to 3c are Coated with TitaniumDioxide in Known Manner by a Wet Chemical Method:

The pigments obtained in Examples 3a, 3b and 3c are, in each case,suspended in totally de-salted water and heated to 75° C. An aqueousTiCl₄ solution is metered in to the suspension. The pH is maintained at2.2 throughout the addition, using 32% NaOH solution. After addition iscomplete, stirring at 75° C. is subsequently carried out for 30 minutesin order to complete the precipitation.

Starting from the pigments described in Examples 3a to 3c, pigmentshaving a TiO₂ layer about 10 nm thick are obtained, their colours(reflectance) being as follows: Starting material Colour Example ofExample (reflectance) 4a 3a green 4b 3b yellow 4c 3c reddish

In addition, the coating with TiO₂ can result in more intense colours.

b) If Desired, an SiO₂ Layer can be Applied to the Pigments Obtained inthat Manner:

For that purpose, the pH of the suspension is increased to 7.5 usingNaOH solution and, over the course of 90 minutes, a soda waterglasssolution (125 g of SiO₂/l) is metered in at 75° C. The pH is keptconstant using 10% hydrochloric acid. After addition is complete,stirring at 75° C. is subsequently carried out for 30 minutes in orderto complete the precipitation.

EXAMPLE 5

Lipstick base having the following composition: Number Substance Amount[%] 1 cera alba 11.4 2 candelilla wax 8.1 3 carnauba wax 3.8 4 LunaceraM 6.0 5 castor oil 38.8 6 Controx KS 0.1 7 aroma oil 1.0 8 Amerlate P2.5 9 OH Ian 1.6 10 isopropyl palmitate 10.1 11 Dow Corning 556 2.8 12Dow Corning 1401 3.3 13 TiO₂ pigment 2.3 14 pigment according to 8.2Example 4a Total 100.0

Substances 8-10 are mixed together, and substances 13 and 14 aredispersed in the resulting mixture. The resulting paste is then passedseveral times through a three-roll apparatus. In the meantime,substances 1-6 are melted, stirred together until homogenous, and thensubstances 7, 11 and 12 are stirred in. The two mixtures are then mixedtogether in the hot state until homogeneous distribution is achieved.The hot mass is then poured into a lipstick mould and allowed to cool.Lipsticks having an intense colour of outstanding light fastness andvery good gloss, and exhibiting no bleeding, are obtained.

1. A method of producing plane-parallel structures of SiO_(y), wherein0.95≦y≦1.8, comprising the steps: a) vapour-deposition of a separatingagent onto a movable carrier to produce a separating agent layer, b)vapour-deposition of an SiO_(y) layer onto the separating agent layer,c) dissolution of the separating agent layer in a solvent, d) separationof the SiO_(y) from the solvent, in which method the SiO_(y) layer instep b) is vapour-deposited from a vaporiser containing a chargecomprising a mixture of Si and SiO₂, SiO_(y) or a mixture thereof, theweight ratio of Si to SiO₂ being preferably in the range from 0.15:1 to0.75:1, and step c) being carried out at a pressure that is higher thanthe pressure in steps a) and b) and lower than atmospheric pressure. 2.A method according to claim 1, wherein the SiO_(y) layer in step b) isformed from silicon monoxide vapour produced in the vaporiser byreaction of a mixture of Si and SiO₂ at a temperature of more than 1300°C.
 3. A method according to claim 1 wherein the vapour-deposition insteps a) and b) is carried out under a vacuum of <0.5 Pa. 4.Plane-parallel structures of SiO_(y), wherein 0.95≦y≦1.8, obtainedaccording to the method of claim
 1. 5. Plane-parallel structures ofSiO_(y), wherein 0.95≦y≦1.8, the particles of which have a length offrom 2 μm to 5 mm, a width of from 2 μm to 2 mm, and a thickness of from20 nm to 2 μm, and a ratio of length to thickness of at least 2:1, thecore of SiO_(y) having two substantially parallel faces, the distancebetween which is the shortest axis of the core.
 6. Plane-parallelstructures according to claim 4 wherein the ratio of the thickness tothe surface area of the plane-parallel structures is less than 0.01μm⁻¹.
 7. A method of producing plane-parallel structures of silicondioxide, comprising steps a) to d) as defined in any one of claim 1 andalso the further step: e) oxidation of the plane-parallel structures ofSiO_(y) separated off according to step d), using an oxygen-containinggas, for example air, at a temperature of at least 200° C. to 1000° C.8. A method according to claim 7, further comprising step f) after stepe): f) carrying out dipping, spraying or vapour treatment of theplane-parallel structures of silicon dioxide with at least one organicsilane compound and/or at least one fluorine-containing organic compoundin order to obtain coupling properties with respect to other organiccompounds or for the purpose of producing hydrophilic, hydrophobic orantistatic surfaces.
 9. Plane-parallel structures of silicon dioxide,obtained according to claim
 7. 10. A method of carburisingplane-parallel structures of SiO_(y), comprising steps a) to d) asdefined in claim 1 and also the further step: g) reaction of theplane-parallel structures of SiO_(y), separated off according to stepd), with a carbon-containing gas selected from alkynes, for exampleacetylene, alkanes, for example methane, alkenes, aromatic compounds andmixtures thereof, at from 500 to 1500° C.
 11. A method according toclaim 10, wherein the carburisation is carried out with exclusion ofoxygen.
 12. A method according to claim 10, which further comprises steph) after step g): h) oxidisation of the residual amount of SiO_(y) ofthe plane-parallel structures carburised according to step g), using anoxygen-containing gas, for example air, at a temperature of at leastabout 200° C. up to a maximum of about 400° C.
 13. A plane-parallelpigment obtained by the method according to of claim
 10. 14. Aplane-parallel pigment based on plane-parallel SiO_(z) substrates, whichcomprises, on the surface of the SiO_(z) substrates, a layer comprisingsilicon carbide (SiC), wherein 0.95≦z≦2.
 15. A method for increasing theresistance to abrasion and resistance to impact of the surface of asurface coating or dispersion layer which method comprises adding atleast one plane-parallel structure according to claim 4 to such asurface coating or dispersion.
 16. (canceled)
 17. A pigment according toclaim 14, comprising a further layer of a dielectric material having arefractive index greater than about 1.65.
 18. A pigment according toclaim 17, wherein the dielectric material is selected from the groupconsisting of zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide(ZrO₂), titanium dioxide (TiO₂), carbon, indium oxide (In₂O₃), indiumtin oxide (ITO), tantalum pentoxide (Ta₂O₅), cerium oxide (CeO₂),yttrium oxide (Y₂O₃), europium oxide (Eu₂O₃), iron oxides such asiron(II)/iron(III) oxide (Fe₃O₄) and iron(III) oxide (Fe₂O₃), hafniumnitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO₂), lanthanumoxide (La₂O₃), magnesium oxide (MgO), neodymium oxide (Nd₂O₃),praseodymium oxide (Pr₆O₁₁), samarium oxide (Sm₂O₃), antimony trioxide(Sb₂O₃), silicon monoxides (SiO), selenium trioxide (Se₂O₃), tin oxide(SnO₂), tungsten trioxide (WO₃) and combinations thereof, an irontitanate, an iron oxide hydrate, a titanium suboxide and a mixture ormixed phase of those compounds.
 19. A composition comprising a highmolecular weight organic material and from 0.01 to 80% by weight, basedon the high molecular weight organic material, of a pigment according toclaim
 14. 20. A cosmetic preparation or formulation comprising from0.0001 to 90% by weight of a pigment according to claim 14, and from 10to 99.9999% of a cosmetically suitable carrier material, based on thetotal weight of the cosmetic preparation or formulation.
 21. An ink-jetprinting, textile, coating, printing ink, plastic, cosmetic, glaze forceramics or glass composition which comprises a pigment according toclaim
 14. 22. A plane-parallel pigment based on plane-parallel SiO_(z)substrates, which comprises, on the surface of the SiO_(z) substrates, alayer comprising silicon carbide (SiC) and silicon nitride (Si₃N₄),wherein 0.95≦z<2.
 23. A plane-parallel pigment based on plane-parallelSiO_(z) substrates, which comprises, on the surface of the SiO_(z)substrates; a layer comprising silicon nitride (Si₃N₄), wherein0.95≦z≦2.
 24. A plane-parallel pigment comprising at least one SiO_(z)layer, which comprises, on the top surface and on the side surfaces ofthe SiO_(z) layer, a layer comprising silicon carbide (SiC), wherein0.95≦z≦2.
 25. Plane-parallel structures according to claim 5 wherein theratio of the thickness to the surface area of the plane-parallelstructures is less than 0.01 μm⁻¹.
 26. Plane-parallel structures ofsilicon dioxide, obtained according to claim 7, having a thickness inthe range from 20 to 2000 nm.
 27. A plane-parallel pigment obtained bythe method according to claim 10 having a thickness in the range from 20to 2000 nm.
 28. A plane-parallel pigment obtained by the methodaccording to claim
 12. 29. A plane-parallel pigment obtained by themethod according to claim 12 having a thickness in the range from 20 to2000 nm.
 30. A method for increasing the resistance to abrasion andresistance to impact of the surface of a surface coating or dispersionlayer which method comprises adding at least one plane-parallelstructure according to claim 5 to such a surface coating or dispersion.31. A method for increasing the resistance to abrasion and resistance toimpact of the surface of a surface coating or dispersion layer whichmethod comprises adding at least one plane-parallel structure accordingto claim 9 to such a surface coating or dispersion.
 32. Acorrosion-resistant coating composition, selectively reflecting in theinfra-red, which comprises at least one of the carburised plane-parallelstructures according to claim
 13. 33. A corrosion-resistant coatingcomposition, selectively reflecting in the infra-red, which comprises atleast one of the carburised plane-parallel structures according to claim14.
 34. A method for pigmenting an ink-jet printing, textile, coating,printing ink, plastic, cosmetic or glazing for ceramics and glasscomposition which comprises adding thereto a pigment according to claim14.